Thermal processing torches, such as plasma arc torches, are widely used in the heating, cutting, gouging and marking of materials. A plasma arc torch generally includes an electrode, a nozzle having a central exit orifice mounted within a torch body, electrical connections, passages for cooling, and passages for arc control fluids (e.g., plasma gas). Optionally, a swirl ring is employed to control fluid flow patterns in the plasma chamber formed between the electrode and the nozzle. In some torches, a retaining cap can be used to maintain the nozzle and/or swirl ring in the plasma arc torch. In operation, the torch produces a plasma arc, which is a constricted jet of an ionized gas with high temperature and sufficient momentum to assist with removal of molten metal.
FIG. 1 is a perspective view of a prior art swirl ring 100 for a plasma arc torch. The swirl ring 100 includes two grooves 102, 104 configured to retain an O-ring (not shown) therebetween. The O-ring is used by the swirl ring 100 to prevent unmetered air from entering its swirl chamber and disrupting the plasma gas swirl pattern in the swirl chamber. As shown, each of the grooves 102, 104 is circumferentially disposed on an interior surface 108 of the hollow body of the swirl ring 100. Each of the grooves 102, 104 comprises a consistent wall projecting inward from the interior surface 108 of the swirl ring 100, where the consistent wall supports and locates the O-ring within the swirl ring. To manufacture the grooves 102, 104, a groove tool is typically used to machine an undercut 106 in the body of the swirl ring 100 from the interior surface 108, which increases the time and cost of manufacturing the swirl ring 100.
In addition, prior art swirl rings (e.g., the swirl ring 100 of FIG. 1) are typically made from ceramic-based materials, such as hydrous aluminum silicate (i.e., lava). A ceramic-based material is capable of being machined in its green state, but requires firing to bake the material into a stable ceramic material. This type of ceramic-based material also has unstable composition (e.g., mined organic material) that can result in high defect rates during swirl ring production. Thus suitability testing is needed to determine how each batch of new material behaves during firing operations. Even though other machine-able ceramic materials that do not require firing are available, they are cost prohibitive and are not commonly used to produce swirl rings. Further, because prior art swirl rings can be used in a pure oxygen (O2) environment within plasma arc torches where electric arc ignition occasionally passes across a swirl ring, this causes swirl rings having polymeric materials that contain a carbon chain to readily burn when ignited, which usually results in the destruction of the torch body and possibly the torch receptacle.
Thus, there is a need for swirl rings that can be manufactured with reduced costs and time and have improved properties that allow them to withstand conditions having a combustible operating atmosphere.